Though the births do little to alleviate concern for the park's mountain gorillas, park director Emmanuel de Merode called the discovery "quite phenomenal," according to the AFP news agency.

The Virunga gorillas have "had a growth of about 11 percent in 10 years, less than two percent a year. To get five births in a group of 30 is about 15 percent growth. It's quite tremendous and very unusual," de Merode said.

The rangers' return is the result of de Merode's direct negotiations with rebel leader Laurent Nkunda, whose forces are clashing with the Congolese Army and other militia groups. Since August the conflict has displaced a reported 250,000 Congolese. Despite a current ceasefire, gun battles could be heard near ranger headquarters Thursday night, the AFP reported.

Infamous for a series of gorilla murders in 2007, Virunga is Africa's oldest national park and home to about 200 of the world's 700 surviving mountain gorillas. (Read "Who Murdered the Virunga Gorillas?" from National Geographic magazine.)